Ellesmere Island Driftwood

It turned out that the age of Ellesmere Island ice shelves is estimated by driftwood located on the shore. an age of ~3,000 years is estimated for the Ward Hunt ice shelf (in which a crack recently developed) based on driftwood located onshore. I haven’t seen corresponding information on the Ayles ice shelf (which actually has broken up.)

In attempting to evaluate how much weight to put on absence of upbeach driftwood as an ice shelf dating method, I ran across a very interesting article, Dyke et al 1997, online here entitled Changes in Driftwood Delivery to the Canadian Arctic Archipelago: The Hypothesis of Postglacial Oscillations of the Transpolar Drift, which sheds light on how much weight to place on presence/absence of driftwood upbeach of modern ice shelves.
Before discussing the interesting questions of the Transpolar Drift (an Arctic current), I’ll first present Dyke et al Figure 4 which bears fairly directly on assessing driftwood presence/absence as an ice shelf dating method. Their Figure 4 shows a census of radiocarbon dated driftwood from the north shore of Ellesmere Island in 250-year intervals. In the last 12 250-year periods going back to 3000 BP, 4 periods had 0 pieces of driftwood and 5 periods had only 1 piece of driftwood.

So, as a start, there would be a considerable randomness to the presence/absence of piece of driftwood in any given 250-year period and it would be extremely difficult to place a lot of statistical significance on the absence of a piece of MWP driftwood purely on statistical grounds. (There are some other issues relating to E-W movement of the Transpolar Drift and to driftwood in Svalbard that I’ll get to on another occasion.)

Dyke et al 1997 FIG. 4. Frequency distribution of radiocarbon dates on driftwood from the Arctic Ocean coast of Ellesmere Island. Samples that date “modern” are plotted to the left of 0 years B.P.Now there’s one sample in this diagram that really catches my eye. Most of the samples dated younger than 3000 years are not behind present ice shelves, but one of them is. I wonder where that sample comes from. This one sample could have quite an impact on how one interprets the driftwood information, given the relative scarcity of samples.

Obviously the existence of a “young” piece of driftwood proves that it was delivered upbeach somehow. Given the scarcity of samples, the absence of driftwood “suggests” or “hints” or “indicates” that the ice shelf was present at intervening times (and thus preventing delivery of driftwood upbeach), but the extremely small population of relevant samples leaves open a very significant possibility that the ice shelf could have been temporarily absent, but that no driftwood happened to be delivered upbeach during the open window. Now no one has suggested that temperatures in this area in the MWP were as high as during the Holocene Optimum and, as noted above, even with the crack in the Ward Hunt ice shelf, it would not be possible at present to deliver driftwood upbeach of the Ward Hunt ice shelf anyway.

The process of delivering driftwood to the north coast of Ellesmere Island also raises many interesting issues. Dyke et al observed that virtually all driftwood to the north coast of Ellesmere Island comes from Siberia. This is proven by the ratio of larch to spruce – larch grows in Asia, spruce in North America. Ellesmere Island has a very high larch ratio. They say that the driftwood is incorporated into sea ice in the polynas offshore Siberia (which turn out to be the main “ice factories” in the Arctic – another interesting byway) and that the sea ice transports driftwood across the Arctic in the Trans-Polar Drift.

Dyke et al hypothesize that the terminus of the Trans-Polar Drift has varied considerably through the Holocene. In one extreme, the Trans-Polar Drift exits the Arctic in the Fram Strait east of Greenland and delivers little or no driftwood to the Canadian Archipelago; in another extreme, the Trans-Polar Drift turns west and delivers driftwood to the archipelago.

Driftwood appears to be absent in the Beaufort Gyre but abundant in parts of the Transpolar Drift (TPD), which crosses the Arctic Ocean from the Chukchi Sea to the vicinity of northeastern Greenland. Nearly 300 radiocarbon dates on Holocene driftwood from the Canadian Arctic Archipelago reveal two regions with contrasting histories of driftwood incursion: the region accessible to wood brought into Baffin Bay by the West Greenland Current and the rest of the archipelago, which receives wood from the Arctic Ocean. We hypothesize that when the TPD was deflected westward along northern Greenland, wood was delivered widely to the Canadian Arctic Archipelago; when the TPD exited entirely through Fram Strait via the East Greenland Current, little or no wood was delivered to most of the archipelago, but some continued into Baffin Bay via the West Greenland Current. A split TPD delivered wood to both regions. The regional driftwood incursion histories exhibit multiple maxima and minima that can be explained by this hypothesis. The Larix to Picea ratio of wood arriving in the Canadian Arctic Archipelago has also changed through time. This may indicate varying contributions from Russian versus North American sources, which in turn may indicate variable mixing of wood en route. The inferred discharge paths of the TPD were apparently stable for intervals ranging from several millennia to centuries or perhaps only decades. The last major switch broadly correlates with the onset of Neoglaciation.

Elsewhere they discuss the delivery of driftwood to Ellesmere Isalnd observing the following:

The aggregate distribution of driftwood dates from the Arctic Ocean coast of Ellesmere Island resembles that for the Baffin Bay region (cf. Figs. 3 and 4). However, this similarity is largely due to the effort applied to dating wood behind the ice shelves. When only samples from areas without ice shelves are considered, important differences appear between the records of the two regions. For example, the decline of wood abundance during the late Holocene, a prominent feature of the Baffin Bay record, is not apparent here (cf. Figs. 3 and 4). This part of the archipelago is nearest to wood sources, and the two oldest dated wood samples from the entire archipelago are from here, both from 8.9 ka B.P. (Stewart and England, 1983; Bednarski, 1986; Lemmen, 1988). Driftwood arrived in only moderate abundance until 6.75 ka B.P., when it increased coincidentally with its increase in Jones Sound. Prominent modes of driftwood arrival date from 6 to 5.75 ka B.P. and from 4.75 to 4.5 ka B.P. The strong mode in Jones Sound between 5.25 and 5 ka B.P. correlates with a minimum in the northern Ellesmere record (cf. Figs. 3 and 4).

Driftwood arrived sparsely between 8.6 and 6 ka B.P. when it suddenly, but briefly, increased to one of two middle Holocene maxima, between 6 and 5.75 ka B.P. This modal abundance correlates exactly with the mode for the northern coast of Ellesmere Island (cf. Figs. 4 and 6). Thus this brief event of abundant wood arrival is widely recorded. Similarly, both records display driftwood minima between 5.25 and 5 ka B.P. that, in turn, correlate with the modal abundance in the Baffin Bay region (cf. Figs. 4 and 6 with 3). The mode between 4.75 and 4.25 ka B.P. in the central Arctic appears to be represented in both the northern Ellesmere and the Baffin Bay records. The strong central Arctic mode between 3.75 and 3.5 ka B.P. corresponds with the sharp decline in wood abundance in the Baffin Bay region.

There’s some interesting information on driftwood supply to Svalbard that I’ll try to summarize on another occasion – there’s a MWP peak, which may or may not represent a fluctuation in the Transpolar Drift terminus. While I was doing this, I also noticed some very interesting information on Arctic Ocean paleoclimate proxies (and especially about the relative warmth of the subsurface Arctic Ocean and the reverse thermocline) – again a topic for another day.

So what can we conclude about relative modern-medieval temperatures based on information from the Ayles and Ward Hunt ice shelves based on the evidence so far (and I’ve still got original references to run down on the driftwood samples)? There’s a crack in the Ward Hunt ice shelf – which in itself does not say anything about modern-medieval relationships. None of the “unprecedented” articles give any driftwood information on the Ayles Ice Shelf which has broken up.

There’s at least one “young” radiocarbon-dated piece of driftwood that has been located upbeach of a modern ice shelf. So there’s more to come on this topic.
ARTHUR S. DYKE, JOHN ENGLAND, ERK REIMNITZ and HàÆ”¬°LàÆà’ NE JETTàÆ”¬°, 1997. Changes in Driftwood Delivery to the Canadian Arctic Archipelago: The Hypothesis of Postglacial Oscillations of the Transpolar Drift, ARCTIC 50, 1–16 nn http://pubs.aina.ucalgary.ca/arctic/Arctic50-1-1.pdf

18 Comments

I think that much of the shelf ice out there is not as old as many think it is. I also think there has been lots of confusion between bona fide shelf ice (e.g. glacial ice that has marine survivorship and is shorefast) versus plain old shorefast sea ice (especially sea ice that is fastened to shelf ice). I would imagine that when winds and current conspire, vast areas of shelf ice can end up being scoured away, especially if there are lots of bergs present, over surprisingly short amounts of time (geologically speaking).

An interesting aspect to the Transpolar Drift is that it seems that sea ice is continuously being formed in the Laptev Sea and other Russian polynas and that this sea ice gets transported to the Atlantic by the Transpolar Drift, and that’s how the fresh water flowing to the Arctic in the big Siberian rivers gets circulated.

3000 years is 12 consecutive 250-year bins without driftwood.
Sadlov, I don’t think anyone would be surprised if “much of the ice shelf out there is not as old…” I rather strongly suspect – without adequate evidence – that most of the Ellesmere ice shelf that broke up over the last century dated from the LIA.

The question is about the age of these inshore fragments.

SteveM, you still have not linked the quote you used to start this series of articles. I believe that is from a thread that is off the new comments section, and well down the articles list. IIRC, there are relevant links and comments there – could you please link to where you got that cite, or at least name the thread and comment number?

There is a search function on the upper right of each CA page. You seem to know which quote you have in mind. Kindly do us a favor and fetch the link yourself please. It’s provided in the clicky number on the upper right of every comment.

I used the search function to search CA using each phrase in that quote, and the search returns empty – except for where he quoted it himself.

SteveM quoted that (I think he mis-attributed it, but I’m not sure), and he didn’t cite it. If he’s going to pull a quote out like that (which is fine in itself), it is courtesy at least to link to the source so the context and precious discussion is available.

If I were an Inuit, living in a cold, fuel-scarce environment – and I came upon firewood well north of the tree line, I might be tempted to burn it. I might do this without regard for how inconvenient this might be for future GW skeptics and alarmists. How do we know low sample size means low deposition rate, rather than high gather rate ?

We (in the royal sense) don’t know to what extent observed stands of wood represent 100% the wood deposited on the shore. We also don’t know the age of deposition of the wood, only the age of its growth. What we can say within the certainty of the radiocarbon dating is that the wood on the shore that was sampled ceased growing 3000 years ago.

Any subsequent conclusions regarding the age of deposition and the apparent lack of younger wood need to be based upon inference of other factors. A straightforward conclusion is that circa 3000 years ago there was sufficient open water to permit the deposition of that driftwood. Any other conclusions are “hinted”, “suggested”, etc. Another possible but unlikely scenario based solely on the absence of younger wood is that the the shore was open but there was no arctic ice to trap and transport the driftwood.

If there are thousands of pieces of exclusively 3000 yr old or older driftwood littering the coastline, that would provide a lot more confidence than a hypothetical coastline that once had thousands of pieces of driftwood, but has since been picked clean to leave 4 pieces which all happen to be 3000 years old or older.

If humans are involved, and they did gather wood for fuel or craft use, might there not be a selection bias for younger wood ?

I have no evidentiary basis to take any position, but this isn’t Antarctica, I’d want to know why human intervention should be excluded as a factor.

You said that the C-14 dating tells us that the wood stopped growing 3000 years ago. I’ve seen two main forms of driftwood: freshly fallen logs with branches broken off about 12″ from the trunk [often near a timber source and close to a river], and smooth, well-worn shapes with all of the younger wood abraded away [after an apparently long stretch in the ocean]

It is quite possible that weathered 3000-year old heart wood came from a conifer tree that stopped growing as recently as 2300-2200 years ago. Add transport time to that. This doesn’t “save” the MWP, but it’s food for thought.

I didn’t mean to discount your question in my prior post. My point was that the date of 3,000 ybp tells us that the ice shelf formed at the most 3,000 years ago. Your comment #14 identifies additional uncertainties. My take-away conclusion is that future work in this area ought to investigate these issues and for now we know that the ice shelf is no older than 3,000 years.

The Dyke paper is a fascinating read, and it emphasizes what Steve Sadlov stated in the earlier thread – there hasn’t been a lot of work done on arctic ice and even less on arctic driftwood.

Earl,
I didn’t take your response as discounting my thoughts on uncertainty, but as a statement of what we could say was known. Thanks for both responses.

I’d agree that we can almost certainly say that the shelf’s has held its continuous position on the coast for no longer than 3000 years. Ice flows, however, and the shelf probably has seasonal or historic ebb and flow which is not necessarily isotropic. Do we know for certain that the ice could not have made it’s way through the shelf [counterintuitively] ? If this sort of low-frequency ‘diffusion’ were viable, one would expect to find additional pieces of wood within the mass of the shelf, itself.

Re-examining the figure, it looks like there are two (not one as stated in my note) recent pieces of driftwood behind modern ice shelves, including one “modern” piece of driftwood. In fact, there are as many recent (2) pieces of driftwood behind ice shelves as there are pieces of driftwood dating to the millennium 2500-3500BP (also 2).

The rheology of the Ellesmere Island ice shelves might be interesting. Their provenance seems a lot different than (say) Antarctic ice shelves which are (as I presently understand it) primarily seaward extensions of glaciers. The Ellesmere Island ice shelves appear to be fed by sea ice originating offshore Siberia transported by the Transpolar Drift. I wonder if there some kind of flow within the shelf itself (a la glacier).

[…] similar form in Dyke et al (1997), which was discussed at length in a Climate Audit post in 2007 here and here. Funder et al cite Dyke et al 1997 on multiple occasions and use its information in their […]